"""Tiny JSON store (one file, atomic writes, one process-wide lock)."""
from __future__ import annotations

import json
import os
import contextlib
import fcntl
import threading

LOCK = threading.RLock()


class Store:
    def __init__(self, path: str):
        self.path = path
        os.makedirs(os.path.dirname(os.path.abspath(path)), exist_ok=True)
        self.data = {"digests": {}, "submissions": [], "rate": {}, "cursor": 0, "seen_urls": []}
        if os.path.exists(path):
            with open(path, encoding="utf-8") as f:
                self.data.update(json.load(f))

    def save(self) -> None:
        with LOCK:
            tmp = self.path + ".tmp"
            with open(tmp, "w", encoding="utf-8") as f:
                json.dump(self.data, f, ensure_ascii=False, indent=1)
            os.chmod(tmp, 0o600)
            os.replace(tmp, self.path)

    def reload(self) -> None:
        with LOCK:
            if os.path.exists(self.path):
                with open(self.path, encoding="utf-8") as f:
                    self.data.update(json.load(f))

    @contextlib.contextmanager
    def tx(self):
        """Cross-process transaction: lock file, reload from disk, mutate self.data, save.
        The web server, mailbox worker and daily job are separate processes sharing one file."""
        with LOCK:
            with open(self.path + ".lock", "a") as lk:
                fcntl.flock(lk, fcntl.LOCK_EX)
                try:
                    self.reload()
                    yield self.data
                    self.save()
                finally:
                    fcntl.flock(lk, fcntl.LOCK_UN)